1. Field of the Invention
The present invention relates to a grip scissors commonly used for thread cutting purposes.
2. Description of the Prior Art
Grip scissors (also known as thread-cutting scissors) have been widely used in Japanese kimono making and other sewing jobs. Traditionally, a pair of grip scissors comprises a generally U-shaped spring portion which is manually grasped, and a pair of blade portions formed integrally with the respective free ends of the U-shaped spring portion. Each of the blade portions has a cutting edge which comes into sliding contact with the cutting edge of the other blade portion.
Generally, such a pair of grip scissors is made by forging a steel strip to have a U-shaped spring portion and a pair of blade portions. Then, the blade portions are ground to have a pair of cutting edges.
In a natural state, the blade portions partially overlap each other, and the respective cutting edges form an acute angle therebetween. For cutting, the U-shaped spring portion is manually gripped to swing the blade portions to reduce the angle between the respective cutting edges while maintaining sliding contact therebetween. When the U-shaped spring portion is freed of the manual gripping force, the blade portions return to their original positions under the elastic restoring force of the spring portion.
A problem with the one-piece grip scissors described above is that when the spring portion is gripped too strongly, the cutting edge of each blade portion tends to project beyond the back edge of the other blade portion due to over-swing movement of the respective blade portions. Thus, the user's fingers may be injured by the thus projecting cutting edge during a cutting operation.
It is conceivable to eliminate this problem by providing, on the spring portion, an opposed pair of stoppers which come into stopping contact with each other for preventing over-swing movement of the blade portions. However, since the spring portion is made of steel, it is rather difficult to integrally form such a pair of stoppers on the spring portion.
Another problem of the one-piece grip scissors is related to heat treatment of the blade portions. Specifically, the blade portions need be thermally hardened by quenching in order to provide a long lasting cutting ability. However, if the spring portion is integral with the blade portions, the thermal treatment (hardening by quenching) of the blade portions also affect the spring portion. Thus, in the absence of strict temperature control, the spring portion is unexpectedly hardened, thus failing to provide an intended spring performance. Further, the hardened spring portion lacks toughness and fatigue strength, so that cracks may be easily formed after repeated use.
A further problem of the one-piece grip scissors resides in the difficulty of re-grinding the blade portions. Obviously, the cutting edges will wear and lose sharpness after repeated use, so that they must be re-ground from time to time. However, with the one-piece grip scissors, since the blade portions are not separable from the spring portion, the blade portions must be inconveniently separated from each other against the elastic force of the spring portion before re-grinding.
In an attempt to solve these problems, the Japanese Utility Model Laid-open No. 63-189172 proposes a pair of grip scissors which comprises a U-shaped spring member made of resin, and a pair of metallic blade members separate from but connected to the spring member. Specifically, each free end of the U-shaped spring member is formed with an axial receptacle bore, whereas the corresponding blade member has a connecting portion inserted in the axial receptacle bore.
Obviously, the separate type grip scissors described above can eliminate the problems attendant with the one-piece grip scissors. However, the separate type grip scissors still have the following problems.
First, since the depth of the axial receptacle bore must be relative large, it is difficult to realize strict dimensional accuracy of the receptacle bore at the time of molding the resinous spring member. Thus, when the connecting portion of the corresponding blade member is inserted in the receptacle bore, the blade member may deviate slightly from an exact position relative to the other blade member. As a result, positional readjustment of the blade member may be additionally necessary, consequently increasing the manufacturing cost.
Secondly, in order to prevent unexpected removal of each blade member, it is necessary to fix the blade member by pins or screws inserted perpendicularly to the blade member. On the other hand, the blade member itself must be inserted axially into the corresponding receptacle bore. Thus, assembly of the blade member must be performed in two different directions which are perpendicular to each other, and a complicated machine must be used for automation of assembly.
In the third place, it is inevitable that the cutting edge of one blade member is slid against that of the other blade member under the elastic force of the spring member at the time of assembly because the respective blade members must be axially inserted into the corresponding receptable bores. Thus, the cutting edge is likely to be damaged or chipped during the assembling operation. Indeed, this problem has been one of the hurdles which must be cleared for realizing automation of assembly.